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Onsala Space Observatory  |  Superconducting Gravimeter

The Gravity Laboratory

Stone wall and sheet-metal roofed building on an outcrop of crystalline bedrock (low metamorphic gneiss); soil and vegetation layers have been cleared.
(However, to the north and northwest of the building there is forest on soil with a slope gently dipping to the northwest.  This area may have a significant hydrological mass flux.)

When the area was cleared from soil, a 3 m deep and 20 m2 large pocket was uncovered. This pocket was subsequently utilised, and the surrounding rock surfaces prepared such that most of the rain water would collect there. We installed a regulated pump that drains the basin and maintains a water level only some decimeter high and within 1 cm of range. 

SCG is mounted inside an inner cabin, which is passively coupled to the air conditioned volume of the main room.

Concrete pillars 1.5 m high resting on the bedrock surface:
A - in main room, accomodates two FG5's
B - in main room, accomodates one FG5
C - SCG pillar in inner cabin.

The walking floor rests on the outer basement wall throughout.

The building is surrounded by an outer 3 m wide concrete-clad apron on top of a polystyren foam layer; the air conditioning device of the main room supplies air flow through the cellar space, and thereby involves the underfloor rock masses in the heat flow circuit.

Ancillary sensors:
Temporary installation of an SNSN 120-s 3-component seismometer (Swedish National Seismic Netowrk, Uppsala University Dep. of Earth Sciences)

The sensor signals of from the following devices are measured with a multi-channel switich digital multimeter and sampled into a designated database:

In- and outdoor thermometers.


An invar rod, length 5.5 m, anchored at 4 m depth next to pillar C, straddling the depth range of the bedrock where most of the annual temperature variation occurs. The distance between the top of the rod and the C-pillar is monitored with an inductive displacement transducer. 

Temperature sensors (Pt-type) in the C-pillar near bottom and top, and at the bottom of the invar rod.

Ground water sensors - still to be installed.

NEWS pages on observations and events at the OSO Gravimetry Laboratory.

Responsable for this page: Hans-Georg Scherneck